Where to get screws?

my iPhone 3G has a crack on the back case housing right by the dock connector. In fact, it's cracked right where one of the 2 screws are located. As such, one of the screws was able to fall out. I am going to get a new cover, but they do not come with screws. Anyone know where I can get just the one screw? I have seen a few screw sets for like 10 dollars but they have like 20 screws in them. I just need the one.

Any idea how much the apple store owuld charge to replace the back while I wait? I havn't been able to find any sites (Google) that will sell just one. The place that sells the cover said they don't have screws.